The present invention relates to the detection and measurement of corrosive or foreign materials. The invention may be applied generally to the detection of metal-loss by corrosion and/or erosion species in single or multiphase fluids. In particular, the present invention relates to the on-stream detection of metal-loss corrosion and/or erosion during an industrial production process. In other embodiments, the invention may be used to detect unwanted contaminants in an industrial process stream. The actual service environment may be aqueous, hydrocarbon, chemical, or a combination thereof.
Corrosive species involved in the production and processing of crude oil and hydrocarbons may cause metal-loss corrosion of production, transfer, storage, and processing equipment. Other types of corrosion degradation may also occur which do not result in metal loss but which nonetheless affect the integrity of the material of construction. Erosive species typically involve fluid and/or solids turbulence causing metal loss from mechanical actions rather than chemical. For example, these corrosive/erosive species may be hydrocarbon, hydrocarbon containing materials, or aqueous, or combinations thereof. Moreover, streams may be single or multi-phase (solids, liquids, gases). The device of the instant invention can be used to generate an alarm based on remaining metal thickness or mechanical integrity of pressure a boundary thereby enabling maintenance scheduling.
A high performance, relatively low-cost detection of a predetermined amount of material loss or material degradation, as in the instant invention, would enable, for example, optimization utilization of corrosive crudes and corrosion inhibitor additions, and reductions in unplanned capacity loss, turnaround time, and inspection costs due to corrosion-induced equipment failures. For example, the instant invention would provide a direct, low-cost alarm when the corrosion allowance of the process containment has been expended. Additional value is achievable with the instant invention by the detection of tramp materials in a process stream which may be corrosive or problematic for the industrial production process. Further value is achievable with the application to monitoring metal-loss corrosion in equipment used for the extraction of crude oil from subsurface and sub sea deposits. Other operating modes are described where the instant invention can be configured as a pressure or temperature alarm. In these and other services, a by-product of the corrosion is scale or other depositions that are adherent to the containment surface. A feature of the instant invention is that the metal loss measurement is not compromised by these non-metallic depositions.
Current corrosion sensing technologies, for example electrical resistance probes, fall far short of the performance level required to achieve the economic incentives described above. Their shortcoming is that the probes' inherent signal variability caused by thermal changes, conductive deposits, and other factors that affect electrical resistance make them intrinsically unsuitable to provide a quantitative indication of material lost from corrosion/erosion. While conventional electrical resistance probes are based on understood theoretical principles, these probes often provide low reliability and poor sensitivity to corrosion rates due to limitations in their design and manufacture. The typical output is often difficult for estimating a quantitative corrosion rate. Another technology that may be used for this application for the material loss application is known as the corrosion the coupon. In this case, a coupon fabricated from the material of interest is inserted into the process stream. At a predetermined time, it is removed and examined and/or weighed to assess the amount of material that has been lost. A significant drawback of this approach is the safety implication of inserting or removing a coupon from an operating high temperature and/or high pressure industrial process. Another drawback of the current technology is the time lag necessary to adequately detect and verify a change in corrosion rates which can then subject the equipment being monitored to an unnecessarily extended period of high corrosion rates before corrective measures can be implemented.
U.S. Pat. No. 6,928,877 and US application 2006/0037399 both employ resonators and teach a relationship between the resonance frequency and mass change. The relationship taught by the prior art applies the well-known formulae relating oscillator mass to it resonance parameters. In particular, the prior art monitors frequency and Q. A deficiency in the prior art is that a quantitative relationship is not established between the material loss, corrosion product deposition and the resonance parameters of amplitude, frequency, and Q. The instant invention teaches away from the prior art by employing a binary monitoring of the oscillator amplitude or frequency. Continuous trending is not required. Clearly this finding is not obvious in light of the teachings of the prior art. In one embodiment, the instant invention has utilized that the oscillator can be immobilized by a fusing link.
The focus of U.S. Pat. Nos. 6,928,877 and 2006/0037399 is to provide a quantitative estimate of mass loss or deposition. Essentially, both provide an alarming function. The instant invention also provides an alarming function. Unlike the prior art where it is difficult to calibrate and predetermine the range for the alarm trigger, the instant invention has no such ambiguity. Once the fusing element is removed or broken, the instant invention goes into alarm mode. It is not necessary to estimate a range over which this alarm mode may initiate because the precise dimensions of the fused-element are known at the time of fabrication. In 2006/0037399 one approach to alarming is achieved by fabricating a hollow resonator. Then depending on the service, the alarming is achieved by filling or emptying the hollow space when the shell of the resonator holes through. Not only is this fabrication more complicated than the instant invention, but it does not provide a procedure to precisely predetermine the change in resonance parameters or to provide an exact measure of the material loss to achieve the alarm threshold. For the instant invention, the change in resonance parameters coincident with the detection threshold are abrupt.